U.S. Pat. No. 4,781,520 by Balter discloses a polar-coordinate manipulator for positioning a disk sample within a vacuum chamber while it is subjected to ion implantation or measurement procedures. Bellows extend from the polar manipulator to the vacuum chamber into which a sample holder extends. The sample holder remains in contact with the sample throughout its rotation and vertical translations within the vacuum chamber. This apparatus is not well suited manipulating a disk for spectral analysis.
Spectral analysis of disks depends strongly on the angle of incidence that the radiation strikes the disk. Such is the case with ellipsometric evaluation, in which the polarization of electromagnetic radiation is altered by the sample depending on the incident angle of the radiation. If the angle of the sample is changed during the sample measurements significant error is introduced into the method. However, if the angle of the sample relative to the optical measuring device is accurately known and controlled, information about number of disk layers and compositions of those layers can be derived from the spectral data.
For industrial applications the compositions of layers and the number of layers is often known and what is of interest to a manufacture of disk products is the consistency of the films that have been deposited on a disk substrate. Therefore, it is necessary to analyze several location on a disk. This can be accomplished by securing a disk to a rotating platform and rotating the disk and platform relative to a stationary measuring device. Rotating platforms described above are generally suspended by a low friction bearing. Unfortunately, even very precise bearing systems introduce enough angular variation in the sample to cause significant errors in spectral measurements. The angular variation of the planar surface of a disk in apparatus of this type are due to several circumstances; 1) The interacting components of the rotating platform may have been imperfectly machined, potentially causing tilting of the sample. 2) A rotating member may be non-perpendicular to the plane in which the sample is held, once again causing tilting. 3) Friction between rotating and static members of the rotating platform may cause uneven thermal expansion of components, again tilting the sample. Additionally, high precision rotating bearing systems used for rotating stages are very large, are very costly, and they physically prevent an operations or measurements from being performed on the bottom portion of the disk sample supported by the rotating platform.
U.S. Pat. No. 4,226,569 by Gerard et al. discloses a sample loader and leveling apparatus. The loading device secures the disk accurately on the stage, but leveling and rotation of the sample is once again accomplished by rotating sample stage similar to that described above and, therefore, suffers from the same disadvantages when integrated into a disk handling system that requires very repeatable and accurate angular positioning of a planar disk sample.
What is needed is an apparatus that can rotationally manipulate a planar sample on a platform, whereby the angle of the planar surface of the sample is consistently maintained from one position to the next. A possible solution is to rotate the device performing the operation or measurement on the sample relative to a static sample secured on a static platform. This is often cumbersome or impossible, depending on the equipment performing the operation or measurement. Further, moving the equipment will generally introduce far greater inaccuracies in the method of interest than does moving the sample. What is further needed is an apparatus for rotating a disk sample that is small and will allow operations or measurements on both sides of a planar sample, such as a disk, either independently or concurrently.